Manatsu Natsuumi, who was born and raised on a small island, is attending 7th grade at a school in the city during the Spring. The day she moved here from her hometown island, she encounters a mermaid girl, Laura, who had come onshore alone to find the Legendary Warrior Pretty Cure. Laura's home, the Mermaid Kingdom in the Grand Ocean, was attacked by the Witch of Delays who lives in the dark abyss of the sea, and the inhabitants' motivation power was seized. If the motivation power of the humans is also taken away, the world will be in trouble!